1. Field of the Invention
Embodiments of this invention relate to methods and products produced by the methods, where the methods include at least one sequential stretching step between circular or spiralized grooved rollers, or modified circular or spiralized grooved rollers.
More particularly, embodiments of this invention relate to methods and products produced by the methods, where the methods include at least one sequential stretching step between such circular or spiralized grooved rollers and the sequential stretching is preformed according to one of at least six aspects described more fully herein.
2. Description of the Related Art
Sequentially stretched products are well known. They are obtained under use of one or more steps of stretching between mutually intermeshing grooved rollers. The grooves of such rollers can be circular, helical or parallel with the axes of the rollers. Prior and/or subsequent to this grooved roller stretching, the film may be evenly stretched in its longitudinal and/or transverse direction.
The sequentially stretched products consist of differently oriented regions, interspersed with one another. This has importance for tear propagation and puncture properties. The following examples of published patent applications deal with such technology and are relevant in connection with the present invention: U.S. patent application Ser. No. 14/023,120 Rasmussen & Rasmussen; U.S. Publication No. 2012/0033900A1 Fraser et al.; U.S. Publication No. 2012/0039550A1 McPherson et al.; WO 213/116264A2 Borchardt et al.; U.S. Publication No. 2012/0269466A1 Dorsey et al.; and U.S. Publication No. 2013/0209711A1 Borchardt et al.
In the method according to the above mentioned U.S. patent application Ser. No. 14/023,120 one film or several films on top of each other are stretched between grooved rollers in a direction, which is different from, but at the highest 80° different from the predominant original direction of orientation in each film. The crests on the grooved rollers are sufficiently sharp to form a distinct division (as further defined in that application) between film material stretched between the crests, and bands of stretched film material, which have laid on and followed the crests. The sharp edges of the latter have prevented stretching of these bands. This prior art Patent Application specifies 3 different ways of obtaining the angle lower than 80° between the original direction of orientation, and the direction of stretching, namely: The film is extruded in tubular shape with a longitudinal orientation dominating. It may or may not be further stretched in this direction. It is helically slit to form a web with a generally mono-axial orientation under an angle to the new machine direction, and is finally segmentally stretched between grooved rollers with circular grooves (also called Ring Rollers). Two or more such helically slit tubes may here be ring-rolled together after being “sandwiched” with criss-crossing directions or orientations. (In some literature, there is distinguished between “crosslaminate”, in which the plies always are bonded together, and “cross-sandwich” in which the plies may or may not be bonded together). The common ringrolling process will normally be enough to form a pattern of bonding/no bonding, which is claimed to be suitable for tear propagation resistance.
Instead of using helical cutting to obtain angular orientation in the web before ring-rolling, the exit of the extrusion die may rotate to form a spiralized melt orientation in the extruded film. This may be collapsed to form a “cross-sandwich” or crosslaminate.
As under the first described procedure, the single film with angular orientation or the crosssandwich, is finally stretched between ring-rollers with sharp edged crests.
As a third option, the mentioned patent application claims that the angle lower than 80° between the extension of the unstretched bands and the direction of stretching, can be obtained by use of mutually intermeshing grooved rollers with spiralized grooves. This third option has particular importance in connection with the present invention.
The present invention concerns improvements, seen in relation to these inventions, in the technologies relating to segmentally stretched polymer films.